This invention relates to the communication of data over a data communications link. More particularly, the present invention relates to a new and improved technique of phase modulating a reference clock used for transmitting data in a primary data communication channel and thereby embedding a separate secondary data communication channel into the primary data communication channel without reducing the available bandwidth of the primary data communication channel.
A serial data channel transfers data serially from a source to a destination over a serial data communication link. The serial data communication link is typically a wire conductor, radio frequency or optical link that spans a relatively long distance. The data is transferred over the serial data communication link and requires a reference clock at the destination to synchronize itself to the periodicity of the transmitted data. The data is formed from binary data bytes each composed of n binary bits. Each binary bit has a binary data bit value of xe2x80x9c1xe2x80x9d or xe2x80x9c0xe2x80x9d. The transmitter unit of the serial data channel encodes binary data into a primary data transmission signal consisting of a sequence of high and low voltage levels that are transmitted at a periodicity established by a reference clock of the transmitter unit. The binary data bit values xe2x80x9c1xe2x80x9d and xe2x80x9c0xe2x80x9d are usually represented by high and low voltage states. Each binary data byte is transmitted during each clock cycle of the transmitter reference clock resulting in the transmission of n binary bits of the binary data byte during each clock cycle of the transmitter reference clock. Thus, the transmitted signal consists of a series of high and low voltage states in which the period of each voltage state is established by the transmitter reference clock frequency. The receiver unit of the serial data channel receives the signal consisting of a series of voltage levels and decodes the signal into a series of binary data bits representing the binary data encode and transmitted by the transmitter unit. In the process of decoding the signal, a reference clock of the receiver unit reconstructs or synchronizes to the transmitter reference clock, typically by using a phase-locked loop. The phase-locked loop reconstructs the transmitter reference clock from data transition points represented by changing voltage levels in the transmitted signal.
In known present serial data channels, data is transmitted only through a primary data communication channel over the serial data communication link as described above. The data transmitted may include primary data, such as data of a memory block or a disk sector, and secondary data, such as control or status information of the source. Any secondary information must be transmitted through the primary data communication channel, which consumes bandwidth of the serial data communication link. The quantity or bandwidth of the primary data transferred over the serial data communication link is reduced by the secondary information which is communicated over the primary data communication channel.
In other known serial data channels, primary data is transmitted though a primary data communication channel over a serial data communication link, and secondary data is transmitted in a secondary data communication channel over a separate secondary serial data communication link. The secondary serial data communication link typically has a lower bandwidth than the primary serial data communication link and is typically used for transmission of control and status information. The use of the secondary serial data communications link for communicating control and status information preserves the bandwidth of the primary data communication channel but adds cost and complexity related to setting up and using the secondary serial data communication link.
It is with respect to these and other considerations that the present invention has evolved.
One aspect of the present invention relates to a serial data communication link having a secondary data channel in addition to a primary data channel, where the secondary data channel is formed by modulating the reference clock of the primary data channel transmitter with secondary data rather than requiring the use of a separate secondary communications link. The secondary data channel does not diminish the integrity of the primary data channel or reduce the bandwidth of the primary data channel. The secondary data channel can be used to transmit secondary data, such as control and status information, simultaneously with the transmission of primary data over the primary data channel.
In accordance with these and other aspects, the invention includes a method of increasing the amount of data transmitted in a data channel established by transmitting primary data using a reference clock signal. The reference clock signal is modulated with secondary data to form a modulated reference clock signal containing the secondary data. Primary data is transmitted using the modulated reference clock signal and received as received primary data. The modulated reference clock signal and the primary data are recovered from the received primary data. The secondary data is recovered from the recovered modulated reference clock signal.
Other preferred aspects of the method include supplying a data byte value as the secondary data, selecting a modulation frequency signal corresponding to the data byte value, generating a modulation frequency signal having the selected modulation frequency, and combining the modulation frequency signal with the reference clock to form the modulated frequency clock signal prior to transmitting the primary data. Other preferred aspects of the method include demodulating the recovered modulated reference clock signal to form a recovered modulation frequency signal, and converting the recovered modulation frequency signal back into the secondary data.
In accordance with these and other aspects, the invention also includes a data channel having a secondary communication channel embedded in a primary communication channel for increasing the amount of data communicated through the data channel. The data channel includes a transmitter, and a receiver connected by a data link. The data channel also includes a reference clock modulator for modulating a reference clock signal with secondary data to form a modulated reference clock signal. The transmitter transmits the primary data using the modulated reference clock signal to a receiver over the data link. The receiver receives the primary data as received primary data and recovers the primary data and the modulated reference clock signal from the received primary data. The receiver also includes a demodulator and frequency detector which recovers the secondary data from the recovered modulated reference clock signal.
Other preferred aspects of the data channel include a latch for supplying the secondary data as a data byte value, a frequency selector for selecting a modulation frequency corresponding to the data byte value, a frequency generator for generating a modulation frequency signal having the modulation frequency, and a phase modulator for modulating the reference clock signal with the modulation frequency signal. Other preferred aspects of the data channel include a demodulator for recovering the modulation frequency signal from the recovered modulated reference clock signal as a recovered modulation frequency signal, and a frequency detector for converting the recovered modulation frequency signal back into the secondary data.
A more complete appreciation of the present invention and its improvements can be obtained by reference to the accompanying drawings, which are briefly summarized below, by reference to the following detailed description of a presently preferred embodiment of the invention, and by reference to the appended claims.